Hydrodynamic cavitation is the result of a flow constriction wherein a liquid falls below the vapor pressure and forms vapor-filled gas bubbles. If the static pressure then increases and exceeds the vapor pressure, these vapor-filled gas bubbles collapse implosively. During the fluid flow movement, the pressure at certain points decreases to a magnitude under which the fluid reaches a boiling point for this pressure, then a great number of vapor-filled cavities and bubbles are formed. As the vapor-filled bubbles and cavities move together with the fluid flow, these bubbles and cavities may move into an elevated pressure zone. Where these bubbles and cavities enter a zone having increased pressure, vapor condensation takes place within the cavities and bubbles, almost instantaneously causing the cavities and bubbles to collapse, creating very large pressure impulses. The magnitude of the pressure impulses within the collapsing cavities and bubbles may reach ultra high pressures implosions leading to the formation of shock waves that emanate from the point of each collapsed bubble. The cavitation and associated effects are useful mixing, emulsifying and dispersing various components in a flowing liquid. The mixing action is based on a large number of forces originating from the collapsing or implosion of cavitation bubbles.
A hydrodynamic cavitation device may appear similar to an in-line fluid flow static mixers, however, to one skilled in the art a static mixer simply consists of mixing baffles arranged so that when a material is discharged from one baffle, it discharges with a swirling action and strikes the downstream baffle. The fluid flow divides before it passes on to the next succeeding baffle, which again divides the flow into various streams. U.S. Pat. Nos. 4,511,258 and 4,936,689 disclose conventional static mixers. However, such mixers cannot be converted to provide a hydrodynamic cavitation device and are not economically feasible in situations wherein a high flow rate and rapid mixing is required.
Hydrodynamic cavitation takes place during the flow of a liquid under controlled conditions through predefined geometries. The phenomenon results in the formation of hollow spaces which are filled with a vapor gas mixture in the interior of a fast-flowing liquid flow or at peripheral regions of a fixed body which is difficult for the fluid to flow around and the result is a local pressure drop caused by the liquid movement. At a particular velocity the pressure may fall below the vapor pressure of the liquid being pumped, thus causing partial vaporization of the cavitating fluid. During the reduction of pressure, gases which are liberated dissolve in the cavitating liquid. These gas bubbles also oscillate and thus give rise to the pressure and temperature pulses.
It is known that devices exist in the art which utilize the passage of a hydrodynamic flow through a cylindrical flow-through chamber which has a series of baffles confronting the direction of hydrodynamic flow to produce varied cavitation effects. The baffles cause a localized contraction of the flow as the fluid flow confronts the baffle element thus increasing the fluid flow pressure. As the fluid flow passes the baffle, the fluid flow enters a zone of decreased pressure downstream of the baffle element thereby creating a hydrodynamic cavitation field. U.S. Pat. No. 5,492,654 discloses a cylindrical flow-through chamber having internally disposed baffles. In this disclosure the upstream baffle elements have a larger diameter than the downstream baffle elements. Such a device is utilized in an attempt to create and control hydrodynamic cavitation in fluids wherein the position of the baffle elements is variable. The study of hydrodynamic cavitation based up the Rayleigh-Plesset equation has been documented in the paper Hydrodynamic Cavitation for Sonochemical Effects, written by the Chemical Engineering Department, University of Bombay, India (1999).
Although the hydrodynamic cavitation devices exist in the prior art, there is nevertheless a need for improvement in many respects to provide a fluid shearing effect and the ability to modify cavitation effects by use of shear plates installed external the flow tube.